November 23rd, 2015PRIMALIGHT News, Research highlightsJuan Sebastian Totero Gongora 0 Comments

It is a common perception that the presence of disorder influences negatively the properties of a physical system. Nevertheless, there are several cases in which disorder plays a positive role and can be exploited to develop novel applications. In general, the introduction of disorder significantly increases the complexity of the system under examination, but, as is often seen in nature, an increase in complexity also corresponds to a richer physical scenario. As a result, in recent years, great efforts have been devoted to the possibility of harnessing complexity and controlling disorder in optical systems at the nanoscale. An important example is provided by the study of the disorder-induced localization phenomena. The generation of highly localized hotspots plays an important role in many plasmonic applications and is usually achieved by considering symmetric and regular geometries (e.g., nano-tips). However, the investigation of the effects of disorder on a plasmonic system is of great interest, and, in this respect, several studies have been conducted on the localization properties of fractal clusters, particles aggregates, and disordered surfaces. Due to the uncertainty produced by randomness and chaos, the study of these systems requires the development of rigorous theoretical models to treat disorder and complexity. In this chapter a disordered plasmonic is modeled by considering a set of interacting cavities. Differently from previous approaches, the modeling explicitly considers the presence of radiative and dissipative losses, hence providing a model which can be easily generalized to describe many different realistic nanoscale systems. The evolution of the system is investigated by deriving a set of coupled mode (CM) equations ruling the distribution and propagation of energy among the cavities. In the stationary regime, the CM equations can be rewritten as a recursive product of real-valued matrices by applying the transfer matrix formalism. In the presence of disorder, the transfer matrices of the system become random variables, and their general properties can be determined by means of random matrix theory (RMT). These calculation, which are performed by considering a suitable statistical mechanics approach, allow for the detection of an optimal amount of disorder maximizing the degree of localization of the system. The results from the theoretical model can be verified by resorting to numerical ab initio simulations, in which a chain of metallic nanoparticles under external illumination plays the role of a one-dimensional set of open cavities. In very good agreement with the theoretical prediction, the numerical results confirm the existence of an optimal value of disorder which maximizes the localization of energy in the system.

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Read more on SpringerLink.

J. S. Totero Gongora, A. Fratalocchi (2015): Harnessing Disorder at the Nanoscale. In: Bhushan, Bharat (Ed.): Encyclopedia of Nanotechnology, pp. 1-13, Springer, Netherlands, 2015, ISBN: 978-94-007-6178-0.